## Singing Pipes

A great science demonstration used to teach about sound waves

The Singing Tube is a great science demonstration used to teach students about sound waves, as the piece of metal pipe is magically made to sing. Since this demonstration requires the use of fire (a propane torch), it must be done by an adult… with a child-like enthusiasm for making science fun.

### Materials

• Piece of metal pipe about 24 inches long
• 4 inch square piece of metal screen mesh (sometimes called gauze)
• Propane torch
• Stick
• Gloves

# Experiment

1. Fold the piece of heavy wire screen mesh several times to make it just small enough to fit in the metal tube. Use a stick to position the screen about 4 inches from the end of the tube.
2. Use a propane torch to heat the piece of screen for approximately 10 seconds. If you could see the screen (but you can’t), it should be red hot from the torch.
3. Remove the tube from the flame and hold it vertically. The tube should begin to “sing”. Reheat the screen when the sound stops.

Questions:

• Why does the sound stop when you cover the top of the tube with your hand?
• Why does the sound stop when you hold the tube in the horizontal position?
• Do you think changing the size of the tube would change the sound? How? (It’s worthwhile to make several tubes of different sizes to hear the changes in pitch.)

# How Does It Work?

The scientific secret behind this demo is simple –  hot air rises. Okay, the full explanation is a little more complex, but not much. When the screen gets hot, the air molecules surrounding the screen rise. This rising hot air begins to oscillate in the tube and produces the sound. As the screen cools down, the air stops flowing through the tube and the sound stops. Changing the size of the tube also changes the pitch. Covering the top of the tube with your hand stops the flow of air and the sound stops. The same holds true when you turn the tube horizontally because the air can no longer flow through the tube. It’s fun to tip the tube over and pretend to pour the sound onto the floor or into a cup. Pretend to pour the sound back into the tube as you return it to the vertical position.

Doug Hodous from Littleton, Colorado, made a set of Singing Tubes that covered an entire octave (C to C). Instead of playing the bells during the holidays, the science department entertained the staff with songs on their Singing Tubes (I’ll bet the punch at the holiday party was spiked!).